Nickel plating process



United States Patent Ofiice Patented Oct. 20, 1970 3,535,212 NICKELPLATING PROCESS Slavko M. Dobrash, Warren, and William R. Vincent,

Birmingham, Mich., assignors to General Motors Corporation, Detroit,Mich., a corporation of Delaware N Drawing. Filed July 6, 1966, Ser. N0.563,053 Int. Cl. C23b 5/50 U.S. Cl. 204--29 6 Claims ABSTRACT OF THEDISCLOSURE A preplating treatment for nickel plating onto zinc in whichthe zinc is first coated with a film of an alkyl or an alkanolamineprior to immersion into the nickel plating bath.

This invention relates generally to the nickel plating of zinc and, morespecifically, to a preplating treatment for use prior to the actualplating sequence.

The pre-plating treatment of our invention is most significantlyeffective when used prior to practicing the nickel plating processdisclosed and claimed in copending U.S. patent application Ser. No.516,761, Baig, filed Dec. 27, 1965 now U.S. Pat. No. 3,417,005. However,the process disclosed and claimed herein is applicable to other nickelplating processes too. The previously mentioned Baig patent applicationis directed toward a nickel electrodeposition bath and the process forits use. The bath disclosed and claimed therein, briefly described, comprises:

At least 0.53 mole/liter of nickel ion (Ni++); at least 0.45 but lessthan 0.54 mole/liter of citrate ion (C6H507 at least 0.023 mole/liter ofgluconate ion (C H 'OP an ion from the group consisting of Cl-) and (F)for inducing anode corrosion; and, an additive from the group consistingof (NHJ) and (triethanolamine) for relieving stresses in the deposit.

More specifically, the Baig bath comprises;

No'rn.(H+) or (OH-) to adjust pH to 5.0-9.5.

Briefly described, the process disclosed and claimed in theaforementioned Baig application comprises the steps of cleaning the partto be plated; immersing the part into a bath comprising theaforementioned constituents; applying a voltage such as to effect acurrent density from about 10-150 amps/ft. removing the part from thebath and rinsing it.

The aforementioned bath and process effectively produces adherent nickeldeposits on a variety of metals, including zinc. However, we have foundthat the deposit will adhere to zinc significantly better if the zinc ispretreated immediately prior to its immersion into the plating bath. Byzinc, we mean to include not only the pure metal, but also alloysthereof having a zinc content in excess of 50% by weight.

It is, therefore, an object of our invention to effect a more stronglyadherent nickel deposit on zinc substrates.

It is a further object of our invention to improve the process for theelectrodeposition of strongly adherent nickel deposits on zincsubstrates, which process is described and claimed in U.S. patentapplication Scr. No. 516,761, Baig, filed Dec. 27, 1965 now U.S. Pat.No. 3,417, 005.

These and other objects of our invention will become apparent from thedetailed description which follows.

Briefly stated, our invention comprises immersing a Zinc article into anickel complexing film-forming alkyl or alkanol amine immediately priorto the immersion of the article into the nickel plating bath. By nickelcomplexing film-forming alkyl or alkanol amine, we mean to include suchcompounds as the methyl, ethyl, and propyl amines, the methanol,ethanol, and propanol amines, and the ethylene and propylene diaminesand derivatives thereof, such as ethylene diamine tetracetic acid.Aqueous solutions of triethanolamine have been found to be significantlyeffective. In our preferred process for nickel plating zinc base diecastings, we immerse them for 15-30 seconds in a 2-10% by volumesolution of triethanolamine and then electroplate them with the bathdisclosed as preferred for zinc base die castings in the aforementionedBaig patent application. This preferred Baig bath as disclosed in theaforementioned copending application comprises:

NorE.pH, 6.7-7.5. Temperature, -150 13.

Any nickel salt can be used as a source of nickel ions, such as nickelchloride, nickel fluoborate, nickel sulfonate, or nickel acetate.However, the best results have been obtained using nickel sulfate,commercially available in the 6-hydrate or 7-hydrate form.

Concentrations of less than 2% by volume of triethanolamine improve theadhesion of nickel to zinc, which has been treated therewith. However,the improvement in adhesion does not become significant untilconcentrations in excess of 2% are employed. Concentrations in excess of10% are effective, but not necessary, and in some respects may even beundesirable, as will be discussed hereinafter in conjunction with theundesirable effects incident to drag-out from the pretreatment bath.

The following is a preferred process that is intended merely to serve asa specific example of our invention for producing an improved, morestrongly adherent electrodeposited nickel coating on zinc. An unbuffedzinc die casting such as a door handle was cleaned anodically at acurrent density of about 50 a.s.f. by immersion into a commercialalakline cleaner, such as Northwest #371, and was treated therein forabout one minute at about 150 F. The part was subsequently rinsed inwater followed by a 10 second dip at room temperature in a 4 oZ./ gal.aqueous solution of an acid salt, such as Northwest Actisalt #1, and awetting agent, such as Northwest Addition Agent #9. The acid dip wasfollowed by a water rinse. The part was next dipped for about 30 secondsin a 100 mL/gal. (2.6% by volume) aqueous solution of triethanolamine atroom temperature. Immediately, without rinsing, the thus treated partwas immersed live into a bath comprising:

G./l. Nickel sulfate 142.2 Nickel chloride 29.92 Sodium citrate Sodiumgluconate 29.92 Ammonium sulfate 33.9

The bath had a pH of 7.0 and was maintained at a temperature of about140 F. Live entry at a strike current density of a.s.f. for about 30seconds followed by a normal plating current density of 40 a.s.f. for 14minutes produced optimum coverage and adhesion. A dual chrome layer wasthen applied in the normal and accepted manner. However, the post nickelplating steps chosen are wholly dependent upon the nature of the articlesought to be produced and may comprise any of the conventional platingsequences known in the art.

We prefer to use the lowest concentration of amine which will producethe desired nickel complexing film. This is preferred in order toprevent any substantial dragout and incident buildup of amine in thenickel plating bath. Hence, for example, the Baig bath has a limitedtolerance for triethanolamine as disclosed in the aforementionedapplication. Too high a triethanolamine concentration in the bath tendsto produce a cracked deposit. Hence, by reducing the concentration ofthe amine, e.g., triethanolamine, in the preplating treatment step,continuous plating may be efiected for a longer period of time beforethe nickel plating bath must be decontaminated or replaced. As thelating baths vary, so also will their respective tolerances for amines.Hence, the particular plating bath selected from the many known in theart will, in many respects, dictate not only the particular choice ofamines, but also the optimum concentration for its use with thatparticular bath.

The treatment of our invention forms a film over the surface of thearticle. Exactly what function this film performs is not known. Onepossible explanation is that the film insulates the surface fromoxidation during its traverse from the pretreatment tank to the platingtank and that the film is destroyed upon entry into the plating tank.Another possible explanation may reside in the fact that only compoundswhich are known to complex nickel seem to be effective and that it isthe ability to complex that produces the improved result. We do notintend, however, to be bound by either of these theories.

While we have disclosed our invention in conjunction with a specificembodiment, we do not intend to limit ourselves, except as by recited inthe claims appended herent nickel coating from the nickel salt solutiononto the surface of the zinc article.

2. A process as described in claim 1 wherein said selected compound istriethanolamine.

3. A process as described in claim 2 wherein said nickel salt solutionhas a pH of about 5.0-9.5 and comprises: (a) a nickel ion concentrationof at least 0.53 moles/liter produced from salts selected from the groupconsisting of nickel sulfate, nickel chloride, nickel fiuoborate, nickelsulfonate, and nickel acetate, (b) a citrate ion concentration of atleast 0.45 but less than 0.54 mole/liter of solution, (c) a gluconateion concentration of at least about 0.023 mole/liter of solution, (d) anion for inducing anode corrosion selected from the group consisting ofchloride and fluoride, and (e) an additive for reducing stress in thedeposit selected from the group consisting of ammonium ions andtriethanolamine.

4. The process as claimed in claim 1 wherein the concentration of saidnickel complexing compound is about 210% by volume, the balance beingwater.

5. The process as claimed in claim 4 wherein said complexing compound istriethanolamine.

6. The process as claimed in claim 5 wherein the nickel salt solutionhas a pH of about 5.09.5 and comprises: (a) a nickel ion concentrationof at least 0.53 mole/liter produced from salts selected from the groupconsisting of nickel sulfate, nickel chloride, nickel fluoborate, nickelsulfonate and nickel acetate, (b) a citrate ion concentration of atleast 0.45, but less than 0.54 mole/liter of solution, (c) a gluconateion concentration of at least about 0.023 mole/liter of solution, (d) atleast one ion for inducing anode corrosion selected from the groupconsisting of chloride and fluoride, and (e) an additive for reducingstress on the deposit selected from the group consisting of ammoniumions and triethanolamine.

References Cited UNITED STATES PATENTS 2,355,070 8/1944 Harford 204493,082,156 3/1963 Brown 20449 3,417,005 12/1968 Baig 20432 WINSTON A.DOUGLAS, Primary Examiner O. F. CRUTCHFIELD, Assistant Examiner US. Cl.X.R. 204-32, 49

